This invention relates to a variable resistor used in an electric, and more particularly, to a sliding resistor.
A conventional sliding resistor is constructed such that a rectangular metal case, having a groove which is rectangular in cross section, is fitted to a base plate, and a rectangular slider is slidably received in the groove. Provided at the bottom plane of the slider is a forked contact piece formed of a leaf spring. The contact piece abuts on a resistance element mounted on the base plate, resulting in that the reaction force or bias force generated by the abutment enables the rectangular slider to be pressed against the rectangular inner wall of the groove of the metal case. In order to permit a smooth sliding of the slider within the metal case, the periphery of the slider must be in good contact with the inner wall of the groove of the metal case. The conventional sliding resistor described is not satisfactory in this respect because both the periphery of the slider and the inner wall of the groove of the metal case exist on the horizontal plane. Specifically, this construction renders it difficult to permit the reaction force or bias force generated by the abutment mentioned to bring the periphery of the slider in good contact with the inner wall of the groove of the metal case, leaving an undesirable clearance therebetween. Because of the presence of the clearance, the slider tends to make undesirable shakings or joltings when moved for the adjustment of the electric resistance, resulting in irregular sliding motion and uneven sliding force.
A sliding resistor intended to remove the above drawback is known to the art. In this case, an assembly consisting of a liner and a leaf spring is provided in the undesirable clearance in question. Indeed, the bias force of the leaf spring enables the liner to make a good contact with the periphery of the slider, thereby eliminating the undesirable clearance. But, troublesome mounting work of the leaf spring and the liner is required for producing the sliding resistor of this type, resulting in a decreased manufacturing efficiency. Further, the requirement of the indispensable parts, such as the leaf spring and the liner, leads to a higher manufacturing cost of the sliding resistor.